Poly(isobutylene-co-isoprene), or IIR, is a synthetic elastomer commonly known as butyl rubber which has been prepared since the 1940's through the random cationic copolymerization of isobutylene with small amounts of isoprene (1-2 mole %). As a result of its molecular structure, IIR possesses superior air impermeability, a high loss modulus, oxidative stability and extended fatigue resistance.
Butyl rubber is understood to be a copolymer of an isoolefin and one or more, preferably conjugated, multiolefins as comonomers. Commercial butyl comprise a major portion of isoolefin and a minor amount, not more than 2.5 mol %, of a conjugated multiolefin. Butyl rubber or butyl polymer is generally prepared in a slurry process using methyl chloride as a vehicle and a Friedel-Crafts catalyst as part of the polymerization initiator. This process is further described in U.S. Pat. No. 2,356,128 and Ullmanns Encyclopedia of Industrial Chemistry, volume A 23, 1993, pages 288-295.
CA 2,418,884 and 2,458,741 describe the preparation of butyl-based, peroxide-curable compounds which have high multiolefin content. Specifically, CA 2,418,884 describes the continuous preparation of IIR with isoprene levels ranging from 3 to 8 mol %. Halogenation of this high multiolefin butyl rubber produces a reactive allylic halide functionality within the elastomer. With these elevated levels of isoprene now available, it is possible, in principle, to generate BIIR analogues which contain allylic bromide functionalities ranging from 3 to 8 mol %. Conventional butyl rubber halogenation processes are described in, for example, Ullmann's Encyclopedia of Industrial Chemistry (Fifth, Completely Revised Edition, Volume A231 Editors Elvers, et al.) and/or “Rubber Technology” (Third Edition) by Maurice Morton, Chapter 10 (Van Nostrand Reinhold Company © 1987), particularly pp. 297-300.
The presence of allylic halide functionalities allows for nucleophilic alkylation reactions. It has been recently shown that treatment of brominated butyl rubber (BIIR) with nitrogen and/or phosphorus based nucleophiles, in the solid state, leads to the generation of IIR-based ionomers with interesting physical and chemical properties (see: Parent, J. S.; Liskova, A.; Whitney, R. A; Resendes, R. Journal of Polymer Science, Part A: Polymer Chemistry 43, 5671-5679, 2005; Parent, J. S.; Liskova, A.; Resendes, R. Polymer 45, 8091-8096, 2004; Parent, J. S.; Penciu, A.; Guillen-Castellanos, S. A.; Liskova, A.; Whitney, R. A. Macromolecules 37, 7477-7483, 2004). The ionomer functionality is generated from allylic halide sites in the BIIR. A greater quantity of multiolefin monomer in the butyl rubber used to produce the BIIR potentially leads to more allylic halide sites upon bromination and hence a greater quantity of ionomer functionality following nucleophilic substitution. The physical properties of ionomers generated from BIIR having a higher multiolefin content are superior to those of their non-ionomeric and/or low multiolefin counterparts.
Polymer nanocomposites is a rapidly expanding, multidisciplinary field that represents a radical alternative to conventional-filled polymers or polymer blends. Polymer nanocomposites are formed by the incorporation of nanosized inorganic fillers into a polymer matrix. Hybrid materials reinforced with neat and/or organically modified high aspect ratio plate-like fillers represent the most widely studied class of nanocomposites. Strong interfacial interactions between the dispersed layers and the polymer matrix lead to enhanced mechanical and barrier properties over the conventional composite. Among the many areas of polymer nanocomposites research, the tire industry has become particularly interested in high aspect ratio fillers. Recent studies have shown that the addition of high aspect ratio fillers in tire inner liner formulations have shown an increase in impermeability of up to 40% (see, for example, U.S. Pat. No. 7,019,063 B2).
Maximizing high aspect ratio fillers to their highest potential requires the correct morphology, making the selection of both the polymer and the filler critical. Polymer intercalation into the platelet galleries, delamination and exfoliation of the platelet and the anisotropic alignment of plates in the rubber matrix must be achieved. In order to accomplish at the very least the intercalation and delamination, it is advantageous to establish a chemical link between the polymer matrix and the filler surface.
Although it may be speculated that the charge properties of ionomers may be useful in establishing the desired chemical link, it is unclear to what extent this will result in improved physical properties in the nanocomposite articles. Although low multiolefin BIIR has been used in the above prior art to generate ionomers that have then been incorporated into nanocomposites, these nanocomposites were unvulcanized and did not benefit from the high degree of ionomeric functionality provided by having a high multiolefin content in the BIIR starting material. Experimental investigation is required to determine the effect of vulcanization and ionomer content on the tensile strength, cure reactivity and/or impermeability of cured nanocomposite articles.